Process for binding of dust in mines

ABSTRACT

PROCESS FOR BINDING OF DUST IN MINES USING FINELY POWDERED HYGROSACOPIC SALTS WHICH ARE APPLIED TO THE SURFACES OF THE GALLERIES AND ARE DISTINGUISHED BY THE ADDITIONPRIOR TO THEIR APPLICATION-OF 1 TO 20% BY WEIGHT RELATED TO THE QUANTITY OF THE HYGROSCOPIC SALT, OF FINELY DISTRIBUTED WATER, WHEREBY THE FINAL PRODUCT IS TO CONTAIN 74 TO 90% BY WEIGHT OF HYGROSCOPIC SALT.

' 3,657,135 PROCESS FOR BINDING OEDUST IN MINES Hans Lewer, Waldstr'. "53,-Witten-Annen, Germany; Hanspeter Dust, Deutz Kalkerstr. 66, Cologne-Deutz, Germany; and Martin Thoennes, Farnweg 20, Bergisch Gladbach, Germany No Drawing. Filed Mar. 13, 1970, Ser. No. 19,514 Claims priority, application Germany, Mar. 26, 1969, P 19 15 333.4 Int. Cl. C09k 3/22 US. Cl. 252-88 10 Claims ABSTRACT OF THE DISCLOSURE Process for binding of dust in mines using finely powdered hygroscopic salts which are applied to the surfaces of the galleries and are distinguished by the addition prior to their application-of 1 to 20% by weight related to the quantity of the hygroscopic salt, of finely distrib uted water, whereby the final product is to contain 74 to 90% by weight of hygroscopic salt.

It is a known fact that coal dust in mines is seriously endangering the safety in mines as well as the health of men working underground. Following directives of the mining authorities mines take comprehensive safety measures. Coating the wooden covering in mines with a layer of hygroscopic salts, to which adhere dust particles hovering in the air-current, thus rendering them harmless, has proved to be particularly effective. Moreover, the salt layer applied renders the wooden covering resistant against fire and putrefaction.

The object of the DBP 1,243,129 (German patent) is a process for the binding of dust in coal mines whereby such dry, finely powdered hygroscopic salts, with or without the addition of wetting agents, are spread on the surface of the galleries.

The salt particles gradually extract moisture from the air in the mines and deliquesce, thus forming the above mentioned dust-binding layer. Although this process has the advantage, as compared with older processes whereby the dust-binding layer is applied in the form of pastes or solutions, that the considerable amounts of water, necessary for the manufacture of pastes and solutions, do not have to be transported, it cannot be overlooked that this salt-dust process has another disadvantage. Applying powdery hygroscopic substances small quantities of very fine particles of these substances are carried away by the aircurrent, bothering and hampering miners exposed to such an air-current. For this reason the mining authorities stipulated that such powdery dust-binding agents are to be applied during shifts when only a reduced number of men or none at all are working. Consequently, attempts were made to absorb or precipitate the salt dust carried away by the air-current, making it possible to apply the salt layer at any time i.e. regardless of change of shift etc. It was also tried to seal up galleries with filter mats. But, apart from the work and expenses connected therewith, it is impossible, to obtain the perfect screening of galleries in which conveyor belts are installed.

Attempts were also made to precipitate, in a zone of water-fog, the salt dust floating in the air. This process, too, requires additional expenses and the substantial amounts of water reaching floor and air-current often cause undesirable side-effects (see: Merkblatt fiir die Anwendung des Chlorcalcium-Montan-Pulvers, Sections 5 and 5.1, of the Bituminous Coal Mining Association, Essen, Germany 1967). In both cases the precipitated dust-binding particles are prevented from fulfilling their task properly.

Uni sd States Patsflt 0 Therefore, a process was looked for which, without the necessity of additional large investments would stop the appearance of very fine particles floating in the aircurrent behind the dust-binding zone.

The process found consists of adding finely distributed water to the hygroscopic saltsprior to their applicain quantities of 120% by weight, in particular 6% by weight, related to the quantity of the hygroscopic salt, whereby the final product is to contain 74-90% by weight, preferably to by weight, of a hygroscopic salt. If the hygroscopic salts, such as calcium chloride, magnesium chloride or their mixtures, are not applied pure, but mixed with inert materials like stone-dust, dried or ground clay or clay minerals, natural or synthetic calcium sulphate or calcium carbonate, boiler ash, industrial dust with a low SiO -content, the quantity of water to be sprayed on is then determined by the water absorption capacity of the mixture; lump formation must be avoided.

If mixtures of hygroscopic salts and inert materials are used, it is possible, to work the necessary amount of Water and the inert material into the mixture simultaneously. It is advantageous to use inert materials which can be admixed in filter-moist condition as, for example, waste gypsum obtained in phosphoric acid production. The water content of the inert materials must then be high enough to meet the aforementioned condition.

If the dust-binding material is to contain also a wetting agent the latter can be added separately or to the water to be sprayed on, i.e. in a suitable composition, the final product thus receiving simultaneously the desired quantity of the wetting agent as well as the amount of water required. According to the effect desired a mixture is prepared consisting of 1 part by weight of a wetting agent and of l, 2 or 3 parts by weight of water. An adequate quantity of it is then added to the hygroscopic salt powder or its mixture with inert materials so that the final product contains, for instance, about 3% by weight of the wetting agent and 3 to 9% by weight of water, both related to the total weight of the final product.

Depending upon the kind of wetting agent used the smell of such hygroscopic salts containing a wetting agent, is sometimes found to be unpleasant. That smell of the wetting agent can be covered up, however, by the admixture of a fragrance to the mixture. Test results show that a quantity of 0.1 to 0.2% by weight, related to the total weight of the final product, is entirely sufficient.

The addition of finely sprayed water leads to the agglomeration and recrystallization between the individual salt-powder particles. Especially the very fine particles are bound in this way and lose, to a very great extent, their ability to float. Hitherto, these particles were carried away by the air-current soon after the application. The salt content of the air-current was measured during and after the application-by-blowing of powdered hygroscopic salts, prepared according to the invention. It was found that the salt content is lower by 88% to 93%, as compared with the application of a salt prepared according to the process known hitherto. In addition, a second effect was observed which could not be foreseen: salt particles which nevertheless get into the air-current have lOst-due to the water sprayed on-the property to cause skin irritation. Test persons who were standing 30 and 50' m. respectively from the blowing apparatus during the application-byblowing of salt powders, prepared according to the invention, were hardly molested by salt particles, During the application-by-blowing of salt powders known hitherto, however, it was unbearable for anybody to stay for some time, even at a distance of 200 m.

This phenomenon of the powder, manufactured according to the invention, is rather surprising, as it is obviously not dependent upon the amount of water contained in the salt powder. The following two salt powders, for example, showed entirely opposite physiological effects. The first one was obtained by grinding calcium chloride 80% and the second one by grinding a substantially dryer Calcium chloride to which, after grinding and according to the invention, water was added increasing its CaC1 -content to the same concentration of 80%. While the former can be applied in the galleries only when the precautionary measures, described above, are taken, miners even working close by are hardly molested when the latter is applied.

The aforesaid will be made clearer yet by the results of some tests carried out:

During the application of salt powder, by blowing, to suppress dust, an analysis of the air at 200 m. from the blowing point showed following results:

when dry salt powder (in accordance with process employed hitherto) was blown: 770 mgms. CaCl /m. air.

when salt powder, onto which water had been finely sprayed (according to the invention), was blown: 65 mgms. CaCl /m. air.

when a dry mixture of salt powder and inert material (in accordance with process employed hitherto) was blown: 600 mgms. CaCI /m. air.

when a mixture of salt powder and inert material, finely sprayed with water (according to the invention), was blown: 39 mgms. CaCI /m. air.

Consequently, the process of the invention makes it possible to cover floors, roofs, etc. of the galleries in mines with a dust binding layer of finely powdered hygroscopic salts, substantial quantities of the salt powder not being carried away by the air-current, excluding also that the small remaining quantities of the salt powder which nevertheless get into the air-current cause irritations on the skin of miners exposed to that air-current. Therefore the application of the dust-binding layer can be carried out at any time without the necessity of having to wait for a shift when only a few miners or none at all are working.

What is claimed is:

1. In a process for binding dust in mines using finely powdered hygroscopic salts which are applied to the surfaces of the galleries, the improvement which comprises adding prior to the application, of 1 to 20% by weight related to the quantity of the hygroscopic salt, of finely distributed water, whereby the final product applied con tains 74 to 90% by weight'of hygroscopic salt. V

2. In the improvement of claim 1, wherein an inert material is added before, after or in addition to the admixture of water to the hygroscopic salt, whereby the relation between the hygroscopic salt and the water, without taking into consideration the inert material, is'to be 74:26 to 90:10. Q a I 3. In the improvement of claim 2 wherein water and the inert material are simultaneously incorporated into the mixture. 3 I 1 4. In the improvement of claim 2 wherein the relation between the hygroscopic salt and the water, without taking into consideration the inert material, is to be :20.

5. In the improvement of claim 2 wherein the necessary amount of water and the inert material are simultaneously incorporated into the mixture.

6. In the improvement of claim 2 wherein a wetting agent is mixed with the water to be finely sprayed on.

7. In the improvement of claim 1 wherein a wetting agent is also added to the water to be finely sprayed on to the hygroscopic salt.

8. In the improvement of claim 7 wherein a wetting agent and a fragrance are admixed with the water to be finely sprayed on.

9. In the improvement of claim 1 wherein 6% by weight of water related to the quantity of the hygroscopic salt is added. p p l 10. In the improvement of claim 1 wherein the final product contains 80 to by weight of hygroscopic salt.

References Cited UNITED STATES PATENTS 102,567 5/1870 Marcus 25288 1,824,588 9/1931' Barstow 25288 FOREIGN PATENTS 1,243,129 6/1967 Germany 25288 JOHN T. GOOLKASIAN, Primary Examiner M. E. McCAMISH, Assistant Examiner US. 01. xR; 

